MB-22781: Update response_headers_test to use meck.
MB-22781: Update response_headers_test to use meck.

Change-Id: I783c2e2ebcdd9f870c2fc29e5c9ab5518dd3f0f7
Reviewed-on: http://review.couchbase.org/80353
Reviewed-by: Ajit Yagaty <670a5cadfa9668cb910cc315f6527868cd5ab42a@couchbase.com>
Tested-by: Amit Krishnan <2d9be4f8a4cc2611c6b78293f950d6eb7edc7196@gmail.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server